In this experiment, we first create a \(^{85}\) Rb Magneto-Optical Trap (MOT) [1]}, [2]}, [3]}. The density of the MOT is about \(10^{10}\)  cm\(^{-3}\) . The temperature of the MOT is about 300 \(\mu \) K. We then excite the atoms to a highly excited state, or a Rydberg state [4]}, at time zero. In this experiment, we use a pulsed dye laser to do the excitation, and we use a wavemeter to monitor the laser output and make sure that the spontaneous emission is suppressed. The pump pulse width from the Nd:YAG laser is about 5-6 ns. The line width of the dye laser is limited by the Fourier transform of the dye laser pulse. We then ionize the atoms using selective field ionization (SFI) [5]}. The rising time of the field ionization pulse is about 5 \(\mu \) s. Different Rydberg states will be ionized at different times. The peak voltage is about 1850 V. We detect the result ions using a pair of Microchannel plates (MCPs). We then collect the ions and display the signal on an oscilloscope. Each peak on the oscilloscope corresponds to one Rydberg state. The oscilloscope signal is exported to a computer and analyzed. For example, we integrate one peak on the oscilloscope to get the number of Rydberg atoms in that particular state. Due to the fact that the field ionization pulse is added after the Rydberg excitation pulse, there is no Stark effect associated with the Rydberg signal collected. Such Rydberg atom detection techniques can be enhanced by combining them with imaging techniques. Recently, Rydberg atoms have been detected by imaging [6]}.
